Mcp-DOM

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start_element_picker

Select DOM elements in a live browser by activating an interactive visual picker with hover highlighting and click selection. Pinpoint exact elements for mutation or inspection without manual code tracing.

Instructions

Activate the interactive visual element picker mode in the live browser with hover highlighting and click selection.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "start_element_picker"
  }
}

Input Schema

Name	Required	Description	Default
`highlightColor`	No	Hex color for hover highlighter (default: #0ea5e9)

Schema Changelog

Changes observed during successful MCP inspections.

First observedv2.0.0Sep 1, 2026

TDQS

A3.7/5.0

Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries full responsibility for behavioral disclosure. It does describe the interactive mode and its visual affordances, but it omits important state-related behaviors: the picker persists until stopped, the browser can be affected by the overlay, and no mention is made of how the selected element is returned or consumed.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, front-loaded sentence with no filler. Every phrase adds meaning: activation, interactivity, visual mode, live browser, hover highlighting, and click selection.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The tool is simple with one optional parameter and no output schema, so the core action is adequately described. However, because the action starts a persistent mode, the description should mention the need to stop the picker or reference the sibling stop_element_picker and get_selected_element to be fully complete for an agent deciding how to sequence calls.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% for the only parameter (highlightColor), so the schema already documents it. The description adds no additional parameter semantics, which is acceptable given the complete schema coverage.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description uses a specific verb ('Activate') and a clear resource ('interactive visual element picker mode'), and adds concrete behavioral details ('hover highlighting and click selection'). This clearly distinguishes it from related tools like stop_element_picker or inspect_live_element.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies usage: it is for activating a picker mode in the live browser. However, it does not explicitly state when to prefer this over alternatives, nor does it mention lifecycle pairing with stop_element_picker or retrieving a selection via get_selected_element.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.